1. Field of the Invention
The present invention relates to applying a photo polymer to a surface and more particularly to a novel method for applying a uniform, holiday-free photo polymer layer on surfaces of both smooth and/or irregular configuration.
2. The Prior Art
The use of photo polymers in the photo fabricating industry is extremely well-known for such valuable uses as production of printed circuits, photo etching, photoengraving and chemical milling and machining. These important processes have historically included a number of conventional steps:
A surface to be etched or milled is first coated with a light-sensitive photo polymer which, when cured, becomes resistant to acids, alkalies or both. Hence, the first photo polymer is commonly called a "resist". Conventionally, a mask is placed over the resist-coated surface so as to leave only selected portions of the resist exposed and unmasked. Depending upon the type of resist used, the light impinging upon the unmasked areas either hardens the resists or degrades the resist so that when the resist-coated part of the surface is subsequently washed in a developer, part of the resist is removed leaving an image defined by the mask on the surface.
The key in producing high quality work of this type is to apply liquid resists uniformly and free from dust, dirt and voids or pin holes, commonly referred to as holidays. The difficulty of properly applying liquid resist is well-known in the industry and numerous techniques have been tried. One somewhat effective prior art method includes completely immersing a surface in liquid resist and slowly removing the surface from the liquid to improve the uniformity of resist thickness. The dipping method has, however, proved to be extremely slow and cumbersome. This is particularly true where the surface is very large or where placement of resist on all parts of the surface is undesirable.
In the face of serious problems encountered in applying liquid resist, at least two major suppliers of resist have abandoned the liquid resist approach and have developed solid film resists which are laminated to the surface. While solid film resists are more expensive than liquid resist, they have gained a strong foothold in the industry because many feel that they can be more reliably applied than liquid resists.
It would therefore be a substantial contribution to the industry to provide a technique of applying liquid resist so as to be uniform and holiday-free.